At present, LCD apparatuses have become more and more popular. LCD apparatuses can be used as displays of desktop and notebook computers, as well as displays of liquid crystal televisions, or in other rapidly developed applications. However, some technological problems such as wide viewing angle, contrast ratio, color saturation, response time and speed and luminance efficiency remain to be solved and/or improved.
With the recent developments of the technology, the above-mentioned problems have been gradually improved except for the luminance efficiency. Referring to FIG. 1A, a known LCD apparatus typically has a backlight module 11 and an LCD unit 12. The LCD unit 12 further includes a lower polarizer 121, a liquid crystal unit 122 and an upper polarizer 123.
Referring to FIG. 1B, the structure of the lower polarizer 121 typically includes a protection layer 121a, a first TAC (triacetyl cellulose) layer 121b, a PVA (polyvinyl alcohol) layer 121c, a second TAC layer 121d, a compensation layer 121f and a release film 121h arranged in order. The second TAC layer 121d is adhered to the compensation layer 121f by a first adhesive agent 121e, and the compensation layer 121f is adhered to the release film 121h by a second adhesive agent 121g. 
In the above-mentioned structure, the backlight module 11 has a light source for generating a light ray 111. The user see an image frame composed of various colors after the light ray 111 passes through the lower polarizer 121, the liquid crystal unit 122 and the upper polarizer 123. However, the light ray 111 generated by the light source of the backlight module 11 is a stray light ray, which is a polarized light ray that does not have a specific polarization pattern, and may include linearly polarized light, circularly polarized light and elliptically polarized light. It has been observed by the inventors of the present invention that when the light ray 111 travels to the lower polarizer 121, only the component of the light ray 111 having the polarization direction parallel to the transmission axis of the lower polarizer 121 can pass through the lower polarizer 121. Thus, the loss in the luminance efficiency is very great, thereby decreasing the luminance efficiency of the LCD apparatus.
Assume that the backlight module 11 respectively generates red (R), green (G) and blue (B) light rays, the R, G and B light rays parallel to the transmission axis are respectively TR//=0.996; TG//=0.994; and TB//=0.992, and the R, G and B light rays perpendicular to the transmission axis are respectively TR⊥=0.004; TG⊥=0.006; and TB⊥=0.008. The transmission rate thereof is as follows:
                              P          ||                =                ⁢                  R          :                      G            :            B                                                  =                ⁢                                            (                                                T                                      R                    ||                                    2                                +                                  T                                      R                    ⊥                                    2                                            )                        2                    :                                                    (                                                      T                                          G                      ||                                        2                                    +                                      T                                          G                      ⊥                                        2                                                  )                            2                        :                                          (                                                      T                                          B                      ||                                        2                                    +                                      T                                          B                      ⊥                                        2                                                  )                            2                                                                        =                    ⁢                      0.496            :                          0.494              :              0.492                                      ,                                  ⁢        and                                T        =                ⁢                                            (                                                0.496                  1                                +                                  0.494                  1                                +                                  0.492                  1                                            )                        /            3                    =                      0.494            .                              
According to the above-mentioned equations, when the absorbing effect of the liquid crystal is not considered, the transmission rate is 49.4%. That is, over 50% of light is wasted, thereby deteriorating the luminance efficiency of the LCD apparatus.
Thus, there is a need to provide an LCD apparatus with the enhanced luminance efficiency and a method for enhancing the luminance efficiency thereof.